This application relates generally to rapid prototyping techniques and, more particularly to a Three Dimensional Printing material and method using particulate mixtures.
The field of rapid prototyping involves the production of prototype articles and small quantities of functional parts, as well as structural ceramics and ceramic shell molds for metal casting, directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective laser sintering process and a liquid binder Three Dimensional Printing process. The techniques are similar to the extent that they both use layering techniques to build three-dimensional articles. Both methods form successive thin cross sections of the desired article. The individual cross sections are formed by bonding together grains of a granular material on a flat surface of a bed of the granular material. Each layer is bonded to a previously formed layer to form the desired three-dimensional article at the same time as the grains of each layer are bonded together. The laser-sintering and liquid binder techniques are advantageous because they create parts directly from computer-generated design data and can produce parts having complex geometries. Moreover, Three Dimensional Printing can be quicker and less expensive than conventional machining of prototype parts or production of cast or molded parts by conventional “hard” or “soft” tooling techniques which can take from a few weeks to several months, depending on the complexity of the item.
Three Dimensional Printing has been used to make ceramic molds for investment casting, thereby generating fully-functional metal parts. Additional uses have been contemplated for Three Dimensional Printing.
For example, three Dimensional Printing may be useful in design-related fields where it is used for visualization, demonstration and mechanical prototyping. It may also be useful for making patterns for molding processes. Three Dimensional Printing techniques may be further useful, for example, in the fields of medicine and dentistry, where expected outcomes may be modeled prior to performing procedures. Other businesses that could benefit from rapid prototyping technology include architectural firms, as well as others in which visualization of a design is useful.
A selective laser sintering process is described in U.S. Pat. No. 4,863,538 to Deckard, which is incorporated herein by reference for all purposes. The selective laser sintering process was commercialized by DTM and acquired by 3D Systems. The selective laser sintering process involves spreading a thin layer of powder onto a flat surface. The powder is spread using a tool developed for use with the selective laser sintering process, known in the art as a counter-rolling mechanism (hereinafter “counter-roller”). Using the counter-roller allows thin layers of material to be spread evenly, without disturbing previous layers. After the layer of powder is spread onto the surface, a laser directs laser energy onto the powder in a predetermined two-dimensional pattern. The laser sinters or fuses the powder together in the areas struck by its energy. The powder can be plastic, metal, polymer, ceramic or a composite. Successive layers of powder are spread over previous layers using the counter-roller, followed by sintering or fusing with the laser. The process is essentially thermal, requiring delivery by the laser of a sufficient amount of energy to sinter the powder together, and to previous layers, to form the final article.
U.S. Pat. No. 5,639,402 to Barlow, incorporated herein by reference for all purposes, discloses a method for selectively fusing calcium phosphate particles that are coated, or alternatively mixed with, a polymeric binder material.
U.S. Pat. No. 5,204,055, to Sachs et al. incorporated herein by reference for all purposes, describes an early Three Dimensional Printing technique which involves the use of an ink-jet printing head to deliver a liquid or colloidal binder material to layers of powdered material. The Three Dimensional ink-jet printing technique (hereafter “liquid binder method”) involves applying a layer of a powdered material to a surface using a counter-roller. After the powdered material is applied to the surface, the inkjet printhead delivers a liquid binder to the layer of powder. The binder infiltrates into gaps in the powder material, hardening to bond the powder material into a solidified layer. The hardened binder also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the previous steps are repeated, building successive cross-sectional portions until the final article is formed. Optionally, the binder can be suspended in a carrier which evaporates, leaving the hardened binder behind. The powdered material can be ceramic, metal, plastic or a composite material, and can also include fiber. The liquid binder material can be organic or inorganic. Typical organic binder materials used are polymeric resins, or ceramic precursors such as polycarbosilazane. Inorganic binders are used where the binder is incorporated into the final articles; silica is typically used in such an application.
U.S. Pat. No. 5,490,962 to Cima, incorporated herein by reference for all purposes, discloses solid free-form techniques for making medical devices for controlled release of bioactive agents.
U.S. Pat. No. 6,397,922 to Sachs et al., incorporated herein by reference for all purposes, discloses a layered fabrication technique used to create a ceramic mold and is incorporated herein by reference for all purposes.
One advantage of using an ink-jet printhead rather than a laser is that a plurality of spray nozzles used to deliver binder to the powder can be arranged side-by-side in a single printhead. In selective laser sintering machines, only one laser, which delivers energy to the powder, is conventionally used. The combination of several spray nozzles increases the speed of liquid binder printing compared to laser-sintering by allowing a wider area to be printed at one time. In addition, the liquid binder printing equipment is much less expensive than the laser equipment due to the high cost of the laser and the high cost of the related beam deflection optics and controls.
However, three-dimensional printing materials may be susceptible to deformation during and after the printing process if sufficient bond strength within and between layers has not adequately developed.
In addition, the powders, especially metallic powders, used in both selective laser sintering and liquid binder techniques present safety issues that render them undesirable for use in an office environment. These safety issues may require special clothing and processing facilities to prevent, for example, skin contact or inhalation of toxic materials. In addition, more expense may be incurred through complying with regulations for the disposal of toxic materials.